Optical depolarizers, optical combiners, and optical isolators are commonly used in optical communication systems and optical measurement systems. An optical depolarizer is generally designed to change a beam of completely polarized light or a beam of partially polarized light into a beam of depolarized light. An optical combiner is a device generally designed to combine two beams of light into one beam of light. An optical isolator is a device generally designed to allow a beam of light to pass through the device in a chosen direction and to prevent the beam of light from passing through the device in the opposite of that chosen direction.
In one aspect, the invention provides an optical depolarizer. The optical depolarizer includes a non-reciprocal combination-device, a birefringent block, and a reflector. The non-reciprocal combination-device has a principal direction and includes a first birefringent wedge, a second birefringent wedge, and a non-reciprocal rotating element. The first birefringent wedge has a first optical axis perpendicular to the principal direction. The second birefringent wedge has a second optical axis perpendicular to the principal direction, and the second optical axis forms a first angle with respect to the first optical axis. The non-reciprocal rotating element is optically coupled between the first and the second birefringent wedge. The non-reciprocal rotating element is designed to rotate the polarization of light passing through the non-reciprocal rotating element by a second angle. The non-reciprocal rotating element can be a Faraday rotator. The birefringent block is optically coupled to the second birefringent wedge. The birefringent block has a third optical axis perpendicular to the principal direction, and the third optical axis forms a third angle with respect to the second optical axis. The reflector is optically coupled to the birefringent block. The optical depolarizer can include a lens that is optically coupled to the first wedge. The optical depolarizer can include a capillary for holding at least a PM optical fiber and an output optical fiber.
In another aspect, the invention provides an optical depolarizer. The optical depolarizer includes a non-reciprocal combination-device, a birefringent block, and a reflector. The non-reciprocal combination-device has a principal direction and includes a first birefringent wedge having a first optical axis, a second birefringent wedge having a second optical axis, and a non-reciprocal rotating element. The non-reciprocal rotating element can be a Faraday rotator. The birefringent block is optically coupled to the second birefringent wedge. The birefringent block has a third optical axis perpendicular to the principal direction, and the third optical axis forms an angle with respect to the second optical axis. The reflector is optically coupled to the birefringent block. The optical depolarizer can include a lens that is optically coupled to the first wedge. The optical depolarizer can include a capillary for holding at least a PM optical fiber and an output optical fiber. The non-reciprocal combination-device is configured for enabling at least the following functions: (1) light entering the second birefringent wedge as an e-ray in a first input direction exits from the second birefringent wedge as an o-ray in the principal direction; (2) light entering the first birefringent wedge as an o-ray in a second input direction exits from the second birefringent wedge as an e-ray in the principal direction; (3) light entering the second birefringent wedge as an e-ray in a reverse principal direction exits from the first birefringent wedge as an e-ray in the reverse principal direction; and (4) light entering the second birefringent wedge as an o-ray in the reverse principal direction exits from the first birefringent wedge as an o-ray in the reverse principal direction.
In another aspect, the invention provides a method of combining first and second polarized light to form depolarized light in an output port. The method includes the step of providing a birefringent block and a non-reciprocal combination-device having a principal direction and a reverse principal direction. The method includes the step of directing the first polarized light to enter the non-reciprocal combination-device in a first input direction and to exit from the non-reciprocal combination-device in the principal direction as first intermediate light. The method includes the step of directing the second polarized light to enter the non-reciprocal combination-device in a second input direction and to exit from the non-reciprocal combination-device in the principal direction as second intermediate light. The method includes the step of passing the first and the second intermediate light through the birefringent block in the principal direction. The method includes the step of reflecting the first and the second intermediate light back through the birefringent block in the reverse principal direction. The method includes the step of directing the first and the second intermediate light to pass through the non-reciprocal combination-device in the reverse principal direction and enter the output port as depolarized light.
In another aspect, the invention provides a method of depolarizing a polarized light to form depolarized light in an output port. The method includes the step of providing a birefringent block and a non-reciprocal combination-device having a principal direction and a reverse principal direction. The method includes the step of directing the polarized light to enter the non-reciprocal combination-device in an input direction and to exit from the non-reciprocal combination-device in the principal direction as intermediate light. The method includes the step of passing the intermediate light through the birefringent block in the principal direction. The method includes the step of reflecting the intermediate light back through the birefringent block in the reverse principal direction. The method includes the step of directing the intermediate light to pass through the non-reciprocal combination-device in the reverse principal direction and enter the output port as depolarized light.
Aspects of the invention can include one or more of the following advantages. Implementations of the invention provide an optical depolarizer and an optical depolarizing combiner that may also function as an optical isolator. Implementations of the invention provides an optical depolarizer and an optical depolarizing combiner that may have small insertion loss, compact size, and reduced manufacturing cost. Other advantages will be readily apparent from the attached figures and the description below.